In the 1980's Teletext services were available in some parts of the United States to display information obtained from an information provider on a television receiver. In the Teletext system, the information provider transmits data that it chooses to send during the vertical blanking interval (VBI) of a television signal. This information includes both text and graphics information. Receivers equipped with a Teletext decoder are able to receive, decode and display this information.
Because the information is transmitted only during the vertical blanking interval of the received television signal, it has a relatively low data rate. Consequently, the information displayed is usually short and simple. Unless the Teletext receiver includes facilities for collecting and storing data over longer intervals, for example overnight while the television receiver is turned off.
Videotex is an interactive version of Teletext. In a Videotex system, data may be provided in substantially the same way as in a Teletext system but it is provided in response to a user request provided via a telephone link. Some Videotex systems, such as the ANTIOPE system used in France, allow data to be sent in a full television channel bandwidth. This results in a bit rate for the data of 6.203 Mbits per second. When Videotex data is being transmitted using the full channel bandwidth, however, normal video signals can not be sent.
Thus, Videotex systems require a television receiver or set-top box which includes a Teletext-like decoder, a one-way telephone link to the information provider and a keyboard that could be used to make the requests. In response to requests from the user, the information provider sends the requested information as encoded data in the video signal, either in vertical blanking interval, as with Teletext, or using the full video bandwidth of a predetermined television signal.
The response to the request is transmitted to all receivers but is addressed to only one. Only that one receiver will receive and decode the information. Even at the relatively high bandwidths described above, it would be difficult for a Videotex system to process requests from many in a timely manner.
Acquisition of the information or data is accomplished only if the television receiver is tuned to the specific channel that carries the transmission. For Teletext systems to obtain more than a trivial amount of information, the television receiver may need to be tuned to the provider channel while the television is not in use, such as overnight.
Other systems exist for providing information or data through the VBI include the Starsight.TM. and Gemstar.TM.. These systems provide Electronic Program Guide (EPG) data over predetermined television channels.
Other service providers, such as DirecTV.TM., Primestar.TM. and Echostar.TM., also provide information through special transport packets in a digital data stream of their signals. This same approach will be used by Digital Cable and Wireless Cable services (MMDS).
With the increased popularity of PCs and the advent of the Internet, licensees of WebTV can obtain and display data from the Internet on their television receivers. These systems use a low-cost computer system and a telephone data link to connect to an Internet server. As such, these systems use HyperText Markup Language (HTML) to provide detailed graphical images and accompanying text. Even with relatively high-speed data link, these systems may need minutes or hours to retrieve and display the amount of data that would normally be found in a newspaper article. The computers used by these systems typically include complex processing hardware (actually a personal computer (PC) without secondary storage). The PC simply displays the information in the way it was sent from the Web Site. This system has a drawback in that the graphical format adds excessive overhead and the attendant throughput problems associated with such large blocks of data. The intelligence for responding to subscriber requests for day/date specific information, the graphical form in which it is displayed, the sorting abilities, etc. are under the control of the Web Server.
Another conventional system, as disclosed in U.S. Pat. No. 5,121,476 to Yee, provides information to a viewer via a television receiver display. In this conventional method the digital data is superimposed on the analog video signal at the video signal source. When the video signal is received by the television receiver, the digital data, which appears as low-level noise in the received image, is extracted and stored in a memory for selective access and display of the data. In this conventional method, the decoder may be internal or external to the television receiver.
In another conventional system, information is provided to the viewer by obtaining data via a link. Such a system is described in U.S. Pat. No. 4,751,578 to Reiter et al. In this system the video signal from the antenna or cable TV source is received and demodulated. The data is then converted into video data and mixed with the demodulated video signal received from the antenna or cable TV input. Finally, the combination of video data and demodulated video signal is re-modulated and sent to the input of the television receiver for further processing and display to the viewer.